Numerical and physical simulation of rapid microstructural evolution of gas atomised Ni superalloy powders

Abstract

The rapid microstructural evolution of gas atomised Ni superalloy powder compacts over timescales of a few seconds was studied using a Gleeble 3500 thermomechanical simulator, finite element based numerical model and electron microscopies. The study found that the microstructural changes are governed by the characteristic temperatures of the alloy. At a temperature below the ' solvus, the powders maintained the dendritic structures. Above the ' solvus temperature but in the solid-state, rapid grain spheroidisation and coarsening occurred, although the fine-scale microstructures were largely retained. Once the incipient melting temperature of the alloy was exceeded, microstructural change was rapid, and when the temperature was increased into the solid+liquid state, the powder compact partially melted and then re-solidified with no trace of the original structure, despite the fast timescales. The study reveals the relationship between short, severe thermal excursions and microstructural evolution in powder processed components, and gives guidance on the upper limit of temperature

Description of Hot Compressive Stress-Strain Curves Using Transfer Functions

“…Newer experimental or supplemental approaches based on virtual fields methods offer a wider range of experimental conditions (high strain rates), and improves accuracy (specimen spatial temperature distribution). Thermal imaging on high temperature compression tests determine spatial distribution of sample temperature, e.g., see Reference [14]. Emerging experimental devices and techniques offer more and more accurate, precise and detailed insights in the hot deformation process, while established physical based models seems to have trouble to convert more precise experimental data in more precise models.…”